Can't get Cell's value while merging cells of same value in gridview in asp.net

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ASP.NET

Gridview

This code is to merge cells with equal values in a GridView
but here i ma getting problem while going through this loop
<pre lang="c#"> for (int i =0; i < row.Cells.Count; i++)
                {
if (row.Cells[i].Text == previousRow.Cells[i].Text)
                {
                    row.Cells[i].RowSpan = previousRow.Cells[i].RowSpan < 2 ? 2 :
                                           previousRow.Cells[i].RowSpan + 1;
                    previousRow.Cells[i].Visible = false;
                }
}

This condition is going to be true for all cells since row.Cells[i].Text="" and previousRow.Cells[i].Text=""
so help me to get real Text values of my grid cells.
here is my Gridview design.

<asp:GridView ID="grdOverallAvg" runat="server" AutoGenerateColumns="false" DataKeyNames=""
                   AllowPaging="True" PageSize="10" Width="100%"
                   OnPageIndexChanging="grdSuggestion_PageIndexChanging"
                    önprerender="grdOverallAvg_PreRender">
                   <HeaderStyle HorizontalAlign="Center" CssClass="GridHeaderClass" />
                   <PagerStyle BackColor="#3B5998" ForeColor="White" HorizontalAlign="Center" />
                   <RowStyle HorizontalAlign="Left" CssClass="GridRowClass" />
                   <EditRowStyle BackColor="#999999" />
                   <AlternatingRowStyle CssClass="GridalternetRowClass" ForeColor="#284775" />
                   <FooterStyle CssClass="GridFooterClass" />
                  <Columns>
                       <asp:TemplateField HeaderText="Faculty" ItemStyle-Width="10%">
                           <ItemTemplate>
                               <asp:Label ID="lblfaculty" runat="server" Text='<%# Eval("faculty") %>'></asp:Label>
                           </ItemTemplate>
                       </asp:TemplateField>
                       <asp:TemplateField HeaderText="Time" ItemStyle-Width="15%">
                           <ItemTemplate>
                               <asp:Label ID="lbltime" runat="server" Text='<%# Eval("time") %>'></asp:Label>
                           </ItemTemplate>
                       </asp:TemplateField>
                       <asp:TemplateField HeaderText="Course" ItemStyle-Width="15%">
                           <ItemTemplate>
                               <asp:Label ID="lblcourse" runat="server" Text='<%# Eval("coursename") %>'></asp:Label>
                           </ItemTemplate>
                       </asp:TemplateField>
                       <asp:TemplateField HeaderText="Start Date" ItemStyle-Width="15%">
                           <ItemTemplate>
                               <asp:Label ID="lblStudname" runat="server" Text='<%# Eval("actualstdate") %>'></asp:Label>
                           </ItemTemplate>
                       </asp:TemplateField>
 </Columns>
                </asp:GridView>